Electronic organ with diverse filters and anti-plop bias arrangement



Sept. 1, 1970 w. v. MACHANIAN ELECTRONIC ORGAN WITH DIVERSE FILTERS vAND ANTI-PLOP BIAS ARRANGEMENT Filed April 24 1968 3 sheets sheet 1(0MP! EX 7v/vE Key r/z, TE I F WWER ENE fw z/ns I RATORS 07 7 FL U TE RAMP!" .32 .34 FILTERS 3g 4 Sept. 1, 1970 w. v. MACHANIAN ELECTRQNICORGAN WITH DIVERSE FILTERS 3 Sheets-Sheet 2 AND ANTI-PLOP BIASARRANGEMENT Filed April 24, 1968 1502a?? 17/11/14 Vflacarzzan Sept. 1,1970 w. v. MACHANIAN 3,526,!M

ELECTRONIC ORGAN WITH DIVERSE FILTERS AND ANTI-PLOP BIAS ARRANGEMENTFiled April 24 3 Sheets-Sheet 3 NMN QWWK

WWWKN w wsv l 3,526,701 ELECTRONIC ORGAN WITH DIVERSE FILTERS ANDANTI-PLOP BIAS ARRANGEMENT William V. Machaniau, Niagara Falls, N.Y.,assignor to The Wurlitzer Company, Chicago, Ill., a corporation ofDelaware Filed Apr. 24, 1968, Ser. No. 723,768 Int. Cl. G10h 1/02 US.Cl. 84--1.11 16 Claims ABSTRACT OF THE DISCLOSURE A portable or Comboelectronic organ having square wave tone generators and direct contactkey switching wherein keying noise or plop is eliminated by chargingcondensers in the circuit to approximately half their normal operatingcharge, and also by the use of waveshaping filters.

In recent years, small groups of musicians playing electric guitars,drums, and often a portable electronic organ, have become quite popular.Such are often known as Combos, and the portable electronic organs usedhave become known as Combo organs. The requirements for such Comboorgans are somewhat different from those of normal electronic organs.For example, conventional electronic organs include loudspeaker systemsand power amplifiers. The acoustic requirements of an enclosure for theloudspeakers has dictated a certain minimum size for such organs. Suchminimum size has not been an inhibiting factor, since it is commonpractice to install such organs in a given location, and to leave themthere.

However, the situation is quite the converse with the so-called Comboorgans. These must be readily portable so that they can be carried fromone location to another just like an electric guitar. Acousticrequirements do not dictate size, since such organs are conventionallyplugged into a guitar amplifier and loudspeaker system. Furthermore,since such Combo organs are generally used by the younger set, and sincethey are looked on as being a rather short-term investment as comparedto the longterm investment in a conventional electronic organ, it isessential that price be kept at a minimum commensurate with quality andother requirements.

It is known in the art that an excellent electric wave for use as a tonesource in an electronic organ is a square wave. This is because such awave has not only a fundamental frequency, but a large number ofharmonics, whereby such waves can be filtered, added, or otherwisetreated for shaping to the desired characteristics. Furthermore, it isknown that the cheapest way of switching such a wave (or any other wavecorresponding to a musical tone) is by the use of a simple single poleor multi-pole switch. Such switching in the past has been prone toaccompaniment by noise known colloquially as keyplop.

In accordance with the present invention, I have found that bymaintaining a square wave of one polarity only, and by chargingcapacitors in a circuit to which the square wave is switched to abouthalf the maximum potential of the square wave, key-plop is substantiallyeliminated. I have found that by coupling the foregoing with properwave-shaping filters, the key-plop can be reduced to the vanishingpoint.

Accordingly, it is an object of the present invention to eliminatekey-plop from electronic organs.

More specifically, it is an object of the present invention to eliminatekey-plop from electronic organs by switching a square wave of constantpolarity into a circuit having the capacitors therein charged tosubstantially United States Patent 3,526,701 Patented Sept. 1, 1970 "icehalf the maximum potential to which they would be charged by the squarewave.

Yet another object of the present invention is to provide an electronicorgan wherein key-plop is eliminated as set forth in the last precedingobject, and further in combination with wave-shaping filters.

A more specific object of the present invention is to eliminate key-plopfrom electronic organs by switching a square wave of constant polaritywherein the square waves corresponding to the plurality of tonegenerators are respectively switched by movable key switches selectivelycngageable with bus bar segments, wherein each bus bar segment has a DC.voltage connected thereto having a potential of about half that of themaximum potential of the square wave.

Other and further objects and advantages of the present invention willbe apparent when considered in accordance with the accompanying drawingswherein:

FIG. 1 is a perspective view of a Combo organ constructed in accordancewith the principles of the present invention, in combination with aguitar amplifier and loudspeaker system;

FIG. 2 is a block diagram illustrating the electrical circuitry of theinvention;

FIG. 3 is a schematic wiring diagram showing the switching andaccompanying filters for the 8-foot stop of the organ;

FIG. 4 is a schematic wiring diagram showing the switching of themixture stop of the present organ;

FIG. 5 is a combined block and schematic wiring diagram illustratingfurther aspects of the present invention;

FIG. 6 is a diagram illustrating the square 'wave from a tone generatorin the present invention;

FIG. 7 is a simplified schematic representation of a low frequencyroll-off filter incorporated in the present invention and used inremoving key-plop; and

FIG. 8 is a simplified schematic representation of the high frequencyroll-01f filter of the present invention.

Turning now to the drawings in greater particularity, and first to FIG.1, there will be seen a portable or Combo organ 1 0 constructed inaccordance with the principles of the present invention. The organcomprises a case 12 of generally rectangular configuration, being ofrather small height, and having a keyboard 14 at the front thereof.Suitable operating controls 16 for switching in various tones, as willbe brought out hereinafter, are provided at the left of the keyboard.The case is supported on a pedestal 18 to which it is detachablyconnected. A foot pedal 20 (sometimes called an expression pedalor aswell pedal) is provided for controlling the overall volume of theorgan, and is connected by means of a wire or cable 22' to electroniccircuits within the case 12.

The output of the organ 10 is connected by means of a lead wire 24 to anamplifier 26, such as a guitar amplifier, and the output of theamplifier 26 is connected to a loudspeaker system identified generallyby the numeral 28, and including any suitable loudspeakers, such as, forexample, loudspeakers 30 indicated in broken lines.

The over-all electrical aspects of the organ 10 are illustrated in blockdiagram in FIG. 2. The organ includes a plurality of tone generators 32,and while these may be of any suitable type, they do provide a squarewave which is always of one polarity. In the present instance, thesquare wave is always positive. As is known in the art, one verysatisfactory way to provide tone generators in an electronic organ is toprovide one octave of stable oscillators, and to have each of thesestable or master oscillators synchronize or control a string of divideroscillators to provide the remaining tone generators at 3 sub-octaveintervals. Flip-flop circuits can be used to produce a very nice squarewave, and this is the preferred type of tone generator in the presentinvention.

The tone generators 32 are connected to key switches 34, and as will beset forth in some detail hereinafter, the key switches are connected inparallel to complex filters 36 and to flute filters 38. As will beunderstood, string, brass, and reed tones are a great deal more complexin harmonic structure than are flute tones. Theoutputs from the filters3:6 and 38 are connected to an amplifier 40 which is in the nature of avoltage amplifier, and this amplifier is connected to a power amplifierwhich may be the amplifier 26 previously referred to, the latter beingconnected to loudspeakers 30 as noted heretofore.

The key switches and filters for the 8-foot flute stop are shown in FIG.3. In an illustrative embodiment of the organ constructed in accordancewith the principlesof this invention, there are forty-nine keys 14, anda corresponding forty-nine tone generators 32. Nine of these generatorsare represented schematically at the top left corner of FIG. 3, and eachis connected through an isolating resistor 42 to a movable contact 44 ofa corresponding one of the key switches 34. Each key switch contact 44is spaced from a bus bar 46, and is respectively movable into engagementtherewith upon depression of a key. As has been noted, the bus bar orrod 46 is long enough to be engaged by any one of the nine key switchesidentified at 44. There is a total of six bus bars, and these bus barsare identified at 46-1 through 46-6. Nine switch contacts are engageablewith bus bar or rod 46-1, as heretofore noted. There are eight switchcontacts engageable with each subsequentbus rod, namely 46-2 through46-6, and the generators associated therewith are indicated immediatelyadjacent the bus rods. For

. simplicity of illustration the key switch contacts associated with thebus rods 46-2 through 46-6 have been omitted, !but it will be understoodthat they are there. Similarly, the bus rods have been somewhatforeshortened. The generators selectively connectable to each bus rodare indicated immediately adjacent thereto.

Each bus rod is shunted to ground by a capacitor 48. Each bus rodfurther has connected thereto a capacitor 50 and a resistor 52 in seriestherewith. The series connected capacitors 50 and resistors 52 from thefirst two bus rods, namely rods 46-1 and 46-2, are connected to ajunction 54a, and this junction is shunted to ground by a parallelcapacitor 56 and resistor 58. The junction 54a fur ther is connectedthrough a capacitor 60 and series resistor 62 to a collector line 64.

Similarly, the series capacitor and resistor from each of the rods 46-3and 46-4 is connected to a junction 54b, similarly shunted to ground andconnected to series capacitor and resistor to the collector line 64. Inlike fashion, the series capacitor and resistor from each of the rods46-5 and 46-6 is connected to a junction 54c, which is likewise shuntedto ground, and connected through a series capacitor and resistor to thecollector line 64.

The collector line 64 is connected to the base of an n-p-n transistor66. The emitter is grounded, and the collector is connected through aresistor 68 to a positive voltage source, indicated as +16 volts. Avoltage divider, comprising resistors 70 and 72, is connected from thecollector to ground, and the junction thereof is connected to the baseto provide bias for the base.

The output of the transistor is taken from the collector through acapacitor 74 and a series resistor 76 to an output line 78 leading tothe amplifier 40. The output line is shunted to ground by a resistor 80,and a movable switch contact 82 is connected to the output line 78. Themovable switch contact 82 is selectively engageable with a fixed switchcontact 84 connected to ground, for shunting the output, to a full-onfixed contact 86 connected to the line 78 for producing full output, orto either of two fixed contacts 88 and 90 respectively con nected toground through resistors 92 and 94 of different values. The position ofthe movable contact 82 is determined by one of the controls 16 on theorgan.

A second output is taken from each rod, and, for example, there is acapacitor 96 connected to the rod 46-1 leading to a resistor 97 which isconnected to a collector line 98. A similar series capacitor-resistorconnection leads to the collector line 98 from each of the subsequentrods 46-2 through 46-6. The collector line leads to a junction 100 whichis connected to the input of an amplifier stage 102. The foregoingcircuitry comprises an 8-foot flute filter, and there is also an inputfrom the 4-foot flute filter to the junction 100, as indicated in FIG.3. The input from the 4-foot flute filter is at onehalf the level oramplitude of the input from the 8-foot flute filter, whereby a step waveis produced which approaches a sawtooth for subsequently producing thereed, string, and brass tones.

The amplifier stage 102 comprises an n-p-n transistor 104, the emitterof which is grounded. The collector is connected through a resistor 106to a positive voltage source indicated as +16 volts. A voltage dividercomprising resistors 108 and 110 is connected from the collector toground, and the junction of these two resistors is connected to the baseof the transistor 104, as is a connection from the junction 100. Theoutput of the amplifier stage 102 is taken from the collector of thetransistor through a capacitor 112 to an output line 114 which leads tothe respective string, brass, and reed filters, as will be notedhereinafter.

One further connection of critical importance remains to be consideredin FIG. 3. Each bus rod has connected thereto a resistor 116 from avoltage or distribution line 118 which is supplied with a small positivepotential, indicated as +0.85 volt. This is to reduce the key-plop aswill be set forth in some detail hereinafter.

Attention should now be directed to FIG. 6 wherein there is shown thewaveform 120 as applied by any of the various generators to a respectivebus rod 46. The waveform is a square wave, and it will be noted that thewave is always of positive potential, the base line or trough thereofbeing at zero volts, and the peak amplitude being a positive 1.5 volts.The broken line indication of .85 volt in FIG. 6 is representative ofthe voltage applied to each bus rod from the voltage distribution line118 through the respective resistors 116. It will be observed that thisis just slightly over half the maximum potential of the square wave.

I have discovered that most of the key-plop is caused by charging of thecapacitors connected to the various bus rods, primarily the capacitors48, 50, and 56, and possibly also including capacitor 60. Withapplication of the positive potential at about the average D.C.potential of the square wave, there is no D.C. shift when a key switchis closed, and hence substantially no key-plop. If a square wave wereused that varied between two fixed D.C. voltages other than zero (eitherof like or opposite sign), the biasing potential applied to the bus barwould be the average of these two voltages to produce the same results.

Key-plop is further reduced, or substantially eliminated by a filteringaction as will be seen with reference to FIG. 7. FIG. 7 comprises asimplified showing of the combination of capacitor 50 shunted to groundby resistor 58 and in series with capacitor 60 shunted to ground byresistor 72. As will be appreciated, the series resistance of resistors52 and 62 has been omitted from this simplified diagram. The circuitwill be recognized as being a low frequency roll-off filter. Thekey-plop is essentially a D.C. or low-frequency transient, and this lowfrequency roll-off filter discriminates against it. The combination ofthe prebiasing of the capacitors and the low frequency roll-off filtersubstantially eliminates key-plop, which is indiscernible in the outputof the organ.

As is known, a flute tone is essentially a fundamental only, with littleor no harmonics. Thus, it is desired to filter out substantially all ofthe harmonics as applied to each bus rod 46 before the output appears onthe line 78. This is illustrated schematically in FIG. 8, which is asimplified representation of some of the circuit elements heretoforedisclosed, and others subsequently to be disclosed. Thus, resistor 42 isin a series path, and is shunted by capacitor 48. Likewise, resistor 52is in a series path shunted by capacitor 56. Connection is then made tothe amplifier including the transistor 66, and from here, connection ismade to the series resistor 76 to another series resistor 122, shuntedby a capacitor 124, and leading to yet another series resistor 126 and ashunting capacitor 128. The circuit of FIG. 8 represents a highfrequency rol-off filter, and the values of the first resistors 42, 52and capacitors 48, 56 are different for each bus rod or pair of bus rodsaccording to the frequencies applied thereto, whereby to eliminate mostof the harmonics and leave a rather pure flute tone.

Turning now to FIG. 4, the mixture amplifier and switching therefor willbe seen to include a grounded bus bar 130 extending the entire length ofthe keyboard. One movable switch or key contract 132 for each key of thekeyboard (a total of 49) normally engages the grounded bus bar 130. Eachswitch has connected thereto four generators, respectively correspondingto the 2% foot, 2 foot, 1% foot, and 1 foot stops of that note, eachgenerator being connected through an isolating resistor 134. Upondepression of a key, the corresponding contact 132 is moved from thegrounded bus bar 130 to a collector bus rod 136. The collector bus 136also extends the entire length of the keyboard, and is engageable byeach of the forty-nine movable switch contacts.

The collector bus is connected to a junction 138 which is coupledthrough a capacitor 140 to the base of an n-p-n transistor 142. Theemitter of this transistor is grounded, and the collector is connectedto a junction 144 which leads through a resistor 146 to a positivevoltage source indicated as +16 volts. A voltage divider is connectedfrom the junction 144 to ground, and comprises series connectedresistors 148 and 150, the junction 152 therebetween being connected tothe base to bias the latter. The output from the amplifier stageincluding the transistor 142 is taken from the junction 144 through acapacitor 154 and a series connected resistor 156 to an output line 158.

Anti-plop bias is applied to the collector bus 136 through a resistor160 connected from the +0.85 volt supply to the junction 138. Theanti-plop bias works the same here as on the 8-foot flute filter stop,and extended discussion therefore is not warranted at this point.

Attention now should be directed to FIG. 5, wherein the tone generatorsare represented generally at 32, and are shown as connected to a 16-footflute filter 162, an 8-foot flute filter 164, a 4-foot flute filter 166,and a mixture filter 168. It will be appreciated that the 8-foot flutefilter 164 comprises all of that which is in FIG. 3 except for theextreme upper right hand corner thereof, while the mixture filter 168includes all of FIG. 4. As has been noted heretofore, and with referenceto the upper right hand corner of FIG. 3 just noted, the 8-foot flutefilter is connected to the junction 100 which is also connected to the4-foot flute filter. This junction is in turn connected to an amplifier170 which includes the transistor 104 and related parts. The 4-footflute filter as connected to the junction 100 presents a signal atonehalf the amplitude of that presented by the 8-foot flute filter 164,and also at twice the frequency. The composite or added wave is of astair-step variety closely approximating a sawtooth, and, as will beappreciated, a sawtooth wave has a complete spectrum of harmonics ascompared with a square Wave which has mostly only odd harmonics. Theamplifier is connected to the output line 114, previously noted, tothree filters, respectively a string 6 filter 172, a brass filter 174,and a reed filter 176, all leading to an output line 178. As will beappreciated, each of the string, brass, and reed filters incorporates aswitch to turn it on or off.

In addition to the flute filter output at 98 to the junction 100, it hasbeen noted previously that the flute filter has an output line 78, andthis leads to an intensity selector switch 180, and specifically amovable switch arm 182 thereof. The switch arm 182 is selectivelyengageable with any of four fixed switch contacts 184, 186, 188, and190. The switch contact 184 is connected to ground to shunt the outputof the 8-foot flute tones to ground, and thereby to produce no S-footflute output. The switch contact 186 is grounded through a relativelylow value resistor 192 to shunt the 8-foot flute output to a lesserextent, while the contact 188 is grounded through a resistor 194 ofhigher value to shunt the 8-foot flute output to a lesser extent. Thecontact is connected direct to the line 196 which forms a continuationof the line 78, and which further leads to the resistor 122 previouslymentioned in connection with the high frequency roll-ofi. filter of FIG.8. This resistor 122 is connected to a junction 198.

The 16-foot flute filter is connected to a switch arrangement andresistor identical to that just disclosed, and the same is true also ofthe 4-foot flute filter 166 and of the mixture filter 168, all beingconnected to the junction 198.

The junction 198 is connected to a high frequency rolloff control 200that aids in determining the purity of the flute tones. This controlincludes the series resistor 126 and shunting capacitors 124 and 128previously mentioned in connection with FIG. 8. The capacitors arerespectively connected to movable switch arms 202 and 204 which areganged together for operation by one of the controls 16. The variousmovable switch arms 182 discussed just above are likewise operated byrespective ones of the controls 16. The movable switch arms 202, 204 arerespectively and selectively engageable with like fixed contacts 206,208, 210, and 212. Each switch contact 206 is connected direct to groundfor providing the maximum effect of the respective capacitor 124 or 128,and hence the maximum high frequency roll-off. Each fixed contact 208 isconnected to ground through a resistor 214 of relatively low value,while each fixed contact 210 is connected to ground through a resistor216 of relatively higher value, progressively to decrease the effect ofthe respective capacitor 124, 128. Finally, each fixed contact 212 is anopen contact, not being connected to anything, whereby to render therespective capacitors 124 and 128 completely ineffective in producingany high frequency roll-off. As will be appreciated, as the highfrequency roll-off is diminished, small amounts of harmonic will bepresent, and this will be almost exclusively odd harmonic due to thesquare wave input. As is recognized, a flute with a degree of suchovertones comprises the tibia stop of an organ.

From the roll-off filter control 200, connection is made to a shuntingresistor 214 and a series resistor 216 to a junction 218. The outputline 178 from the string, brass, and reed filters is connected to thisjunction. From this junction, connection is made to a transistoramplifier stage 220 of generally conventional construction, and having apotentiometer 222 across the output. The slider on the potentiometer iscontrolled by one of the controls 16, and connection is made from it toanother transistor amplifier stage 222, the two stages togetherconstituting the amplifier 40 previously noted. The output from theamplifier 40 is indicated at 224 in FIG. 5, and this goes to the poweramplifier 26 previously mentioned in connection with FIG. 2.

It will now be seen that I have successfully eliminated key-flop from anelectronic organ by utilizing a square wave (varying between zero and apositive value in the illustrative embodiment), and by connecting apotential of approximately the average potential or value of the squarewave to the pick-up or collector from the switches, whereby there is noD.C. shift when a key switch is closed. The eliminationof key-flop isfurthered by the incorporation of a low-frequency roll-off filter,'while a high frequency roll-off filter of adjustable characteristicsconverts the square waves into flute tones.

The specific example of the invention as herein set forth isforillustrative purposes only. Various changes in structure will no doubtoccur to those skilled in the art, and will be understood as forming apart of the present invention insofar as they fall within the spirit andscope ,of the appended claims.

The invention is claimed as follows:

1. An electronic organ comprising means for providing a plurality ofelectrical oscillations respectively corresponding to musical tones,said oscillations being predominantly of one polarity, a plurality ofkeys and a plurality of key switch means respectively operated therebyand respectively connected to said oscillation providing means, outputmeans to which said key switch means are connected and including atleast one capacitor tending to charge with said one polarity uponclosure of said key switch means, and a potential source of said onepolarity connected to said output means to maintain said capacitor atleast partially charged with said predetermined polarity.

2. An electronic organ as set forth in claim 1 wherein the electronicoscillations comprise square waves, and wherein the output meansincludes a filter of which said capacitor forms a part.

3. An electronic organ as set forth in claim 1 wherein the electronicoscillations have a predetermined average potential, and wherein saidpotential source charges said capacitor substantially to saidpredetermined potential.

4. An electronic organ as set forth in claim 3 wherein the electronicoscillations comprise square waves of one polarity only.

5. An electronic organ as set forth in claim 2 wherein said filtercomprises a low frequency roll-off filter.

6. An electronic organ as set forth in claim 2 wherein said filtercomprises a high frequency roll-off filter.

7. An electronic organ as set forth in claim 5, and further including ahigh frequency roll-ofl filter.

8. An electronic organ comprising means for providing a plurality ofelectrical oscillations respectively corresponding to musical tones, aplurality of keys and a plurality of key switch means respectivelyoperated thereby and respectively connected to said oscillationproviding means, a predetermined number of collectors less in numberthan said plurality of key switch means, each of said collectors havingconnected thereto a predetermined subplurality of said key switches, apredetermined number of filters each connected to one of saidcollectors, means combining the outputs of said filters in groups,additional filter means connected to said groups, and output meansconnected to said additional filter means.

9. An electronic organ as set forth in claim 8 wherein said filters andsaid filter means include a low frequency roll-off filter.

10. An electronic organ as set forth in claim 8 wherein said electricoscillations comprise square waves, and wherein said filters and filtermeans include a high fre quency roll-off filter.

11. An electronic organ as set forth in claim 10 wherein said filtersand filter means further include a low frequency roll-off filter.

12. An electronic organ as set forth in claim 11 and further includingmeans for adjusting the high frequency roll-off.

13. An electronic organ as set forth in claim 8 wherein saidoscillations are of predominantly one polarity, and wherein said filtersand filter means include capacitors, and further including a potentialsource of said one polarity connected to said collectors to maintainsaid capacitors at least partially charged with said predeterminedpolarity.

14. An electronic organ comprising means for providing a plurality ofsquare wave electric oscillations respectively corresponding to musicaltones, a plurality of keys and a plurality of key switch meansrespectively operated thereby and respectviely connected to saidoscillation providing means, each key switch means having a plurality ofcontacts corresponding to different organ footages and respectivelyconnected to oscillation providing means of such footages, collectormeans connected to said key switch means according to said footages,means for connecting certain of said output means in predeterminedcombination to add certain footages to produce a square waveapproximating a sawtooth wave, filter means connected to said footageconnecting means to produce complex organ voices, filter means connectedto said collector means for producing the footage voices of an organ,and means for selectively connecting said footage filters and saidcomplex voice filters for combining the footage and complex voices.

15. An electronic organ as set forth in claim 14 wherein the footagefilters include high frequency roll-off means, and means forsimultaneously adjusting the high frequency roll-off characteristics ofsaid high-frequency rolloff filters.

16. An electronic organ as set forth in claim 14 wherein the squarewaves are predominantly of one polarity, and further including apotential source of said one polarity connected to said collector means,said filters including capacitors, and said potential source maintainingsaid capacitors at least partially charged with said predeterminedpolarity.

References Cited UNITED STATES PATENTS 2,842,021 8/1958 Oncley 841.012,953,958 9/1960 George 84l.2.7 X 3,098,407 7/1963 Brand et al 84-1.113,272,906 9/1966 De Vries et al 84l.25 3,300,569 1/1967 Cunningham84-122 3,443,463 5/1969 Campbell 84-1.01

WARREN E. RAY, Primary Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,526,701 Dated S t b 3910 Inventor(s) William V. Machanian It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Col 1, line 23, after "such" insert --groups-;

Col. 5, line 16, change "rol-off" to --roll-off--;

Col. 7, line 28, change "electronic" to --electrical--; Col. 7, line 32,change "electronic" to --electrical--; Col. 7, line 34, after"predetermined" insert --average--; Col. 7 line 36, change "electronic"to -electrical--;

Col 7, line 52, change "switches" to --switch means--; and

Column 8, line 1, change "electric" to --electrical--;

g Officer common of Puma

